The effectiveness of information and communi-cation technology (ICT) monitoring, which links real time field images with soil and environmental data, was evalu-ated by a case study in a cold upland cabbage field. Soil and weather conditions were measured with the ICT mon-itoring system in order to understand the water cycle at the cold upland cabbage field. A fieldserver and soil sen-sors (ECH2O-TE, Decagon Devices) were installed at the cabbage field to measure weather condition, soil temper-ature, soil moisture, and soil electrical conductivity (EC). Soil moisture at the cabbage field was close to saturation during the cultivation season. Possible reasons for the wet soil conditions are that a hardpan with a small saturated hydraulic conductivity exists at depths of 40–45 cm, and the precipitation rate was much larger than the evapotran-spiration rate at the cabbage field. The soil EC revealed that soil solute transfer clearly followed the precipitation pattern. Soil temperature and soil moisture during the win-ter season showed different diurnal variations depending on snow cover and its melting. The real time field im-ages linked with the soil and weather data provided a more complete description of conditions than could be captured with only soil and weather observations. The ICT mon-itoring of soil properties and weather conditions was an effective tool for enhancing the understanding of field con-ditions through the use of real-time field images.
It is essential to simultaneously monitor soil water content (θ) and bulk electrical conductivity (ECa) in field soils for soil salinity assessment. A low-cost ca-pacitance sensor, 5TE (Decagon Devices), can be used to study temporal variations in θ and ECa. Laboratory and field experiments were conducted to investigate the appli-cability of the 5TE sensor to monitor the salinity in the fields damaged with seawater at the time of the 2011 of the Pacific coast of Tohoku earthquake. The dependency of calibration curves on salinity for estimating θ was eval-uated. The salinity effects could be neglected when the so-lution EC (ECw) was lower than 7 dS m−1. The Rhoades model was found to be reasonably accurate to describe the ECa–ECw–θ relationships. Moreover, ECw obtained by the 5TE sensor, combined with the Rhoades model, was positively correlated with EC1:5 (EC of 1 : 5 soil:water ex-tracts). These results suggested that EC1:5 can be estimated from the θ and ECa measurements using the 5TE sensor. Field monitoring using the 5TE sensors revealed that salts in the root zone were sufficiently removed by rainwater during the summer after the damage; thus, EC1:5 values at 0.15 and 0.3 m depths became adequately lower by the end of July. In the following months, EC1:5 values at 0 and 0.3 m depths remained lower than 0.2 dS m−1 during the cultivation period for strawberries from October to April whereas EC1:5 values at 0.45 m depth fluctuated between 0.4 and 0.8 dS m−1. Simultaneous monitoring of θ and ECa, by using the 5TE sensors, can provide highly detailed information concerning temporal variations in soil salinity.
It is known that nitrogen is fixed by algae and photosynthetic bacteria at the surface soil of ponded paddy field. The biological nitrogen fixation is one of the main natural nitrogen supply in addition to the irrigation and rainwater supply. The active location of the bacteria and the amount of fixation, however, have not yet well stud-ied. In this report, at first, we investigated the penetrating depth of sunlight into the surface soil using a solar battery with radiometer. Then, we examined the distribution of to-tal nitrogen content under exposed and shielded conditions to the sunlight at interval of 2 mm from the surface. Total nitrogen contents determined by a NC-analyzer increased only in the uppermost (0 – 2 mm) layer from the ponded surface soil for the exposed condition. Since the sunlight reached down to 1 mm from the soil surface, we concluded that the biological nitrogen fixation occurred only at the thin surface layer with the penetrating sunlight.
Thermal response tests (TRTs) have been widely used to identify thermal conductivity of soils. How-ever, only the first two terms of power-series expansion for the exponential integral, which appears in Kelvin’s line source function used for analyzing data of TRTs, have been used by the conventional method. This method sometimes leads to inaccurate estimation of parameters and long test-ing time. A new method, briefly introduced in this paper, evaluates much higher terms and uses an inverse method to identify thermal conductivity together with a parameter containing volumetric heat capacity. This method also en-ables to identify true thermal conductivities by using early data of TRTs and to reduce testing time. Some cases ap-plied to fields with various conditions are also shown in this paper for further application to soil physics.
The Komesu subsurface dam was constructed along the Pacific shoreline south of Itoman City, Oki-nawa, Japan, to provide a reservoir for groundwater in the Ryukyu Limestone aquifer and to prevent saltwater intru-sion from the sea. At present, residual saltwater remains in the reservoir and has not yet spread out during the past 10 years since the completion of the cut-off wall. Con-tinuous monitoring of the groundwater level and electrical conductivity measurements showed that the electrical con-ductivity of the stored groundwater along the cut-off wall increased drastically during the rainfall events. This find-ing suggests that upward movement of the residual salt-water was associated with the groundwater flow over the cut-off wall, as previous studies have noted.